In a convergent network, both voice-based and data-based telecommunications applications are combined in one packet-oriented network. They thus provide a shared infrastructure for voice-based and data-based telecommunications applications. The transmission protocol frequently used in these types of networks is advantageously the Internet Protocol (IP). The advantage of these types of networks lies in the enhancement of the IP network along with reduced operating costs and the simultaneous possibility of providing real-time services such as video telephony or life-streaming. Since the transmission of data is effected in IP-networks by packet-based means, the services offered through the network are also termed packet carrier services. These include, in particular, integrated enterprise communication with broadband applications, such as web presentations and video conferencing, where such applications constitute user services. With reference to the ISO-OSI layer model, packet carrier services relate to the processes in and between Layers 1 and 3, whereas user services are located on Layers 4 through 7 and ultimately form the interface between the user and the devices, in particular terminals.
Implementation of a convergent network provides the ability to exploit these packet carrier services from mobile and permanently installed communications terminals. In the following discussion, mobile and permanently installed communications terminals are generally identified as terminals.
Real-time transmission of data is characterized by the transmission of a predetermined quantity of data, i.e. data bits, within a predetermined guaranteed time period in the form of a continuous data stream in a specific sequence, where in each case the same number of data elements are transmitted per time interval within this data stream. For real-time transmission, a subjective requirement must furthermore be taken into account since a user expects to be able to receive and reproduce a file transmitted in real time relatively rapidly and without disruption. The data stream in real-time transmission is thus continuous, and thus generally also designated as streaming. To be sure, a specified timing per data packet (time symmetry) is not absolutely necessary. The timing can instead vary and be selected based on each application. Streaming requires logging in to a resource and also acknowledges the end of the transmission.
A network protocol standard designed by the Internet Engineering Task Force (IETF) is known as Mobile IP and allows the users of mobile devices such as notebooks to switch from a wireless-based computer network through a first transmission medium, such as, for example, WLAN (Wireless Local Area Network), to different computer network, and at the same time enables them to retain a static IP address. The standard is described in Recommendation 3GPP TS 23.234. Mobile IP provides an efficient and scalable mechanism for the mobility of computers. The protocol ensures that mobile computers can switch their access point to the Internet yet still retain their static IP address. This ensures that connections of the Transport Layer remain intact when switching networks. Various mobile providers of Mobile IP employ active cyclic checks and/or radio signal measurements for switching to an alternative transmission medium. Mobile IP is based on carrying out bidirectional communication in order to use other transmission paths. Bidirectional communication requires a certain amount of time that is caused by transmission and data processing in the nodes.
In addition, a telecommunications standard is also known as GAN (Generic Access Network), also called UMA (Unlicensed Mobile Access), that expands voice and data transmission, and the IP Multimedia Subsystem/Session Initiation Protocol (SIP) from mobile telephony to IP access networks such as the Internet. GAN here makes possible the convergence of mobile and wire-based Internet telephony. It enables the user to seamlessly switch between WLAN and WAN (Wide Area Network). A GSM/WiFi-capable (Global System for Mobile Communications, WiFi is a radio standard to use WLAN) dual-mode mobile telephone is required for this purpose. GAN provides an approach where as soon a WLAN is detected a mobile-communications terminal establishes a secure IP connection via a gateway through a tunnel to a server of the mobile-communications network operator, this being identified as a GAN controller (GANC). The server acts like a conventional base station of the cellular mobile-communications network. The mobile-communications terminal communicates through a secure link using special protocols (BSSGP, Base Station System GPRS Protocol). From the point of view of the mobile-communications network, switching by the mobile-communications terminal from the GSM transmission medium to the WLAN transmission medium appears as if the mobile-communications terminal has simply switched the base station, as is the case when changing from one mobile-communications cell to another. The GAN standard uses IETF RTCP (Internet Engineering Task Force, Real Time Protocol Control Protocol) information as the trigger to effect switching in the transmission medium. The standard does not specify any mechanism by which a controlled, needs-based switching to WLAN is effected. Instead switching is always done to the alternative transmission medium if this is available. Since WLAN access points are available in increasing number and density, the use of the GAN standard very often results in switching to the second transmission medium. Apart from this, the approach always monitors whether the mobile-communications terminal is located near a WLAN. This results in increased power consumption and to unnecessary signaling traffic in the network due to the frequent switching.